Energy driven surgical tools which apply acoustic energy to tissues can cause tissue effects deep in the body structures through relatively long, narrow passages. For deep and narrow surgery many devices and techniques have been developed and used. For example, cold knife techniques using knife blades or a rotating suction debrider such as marketed by Medtronics have been employed. The latter is an improvement as it removes tissue and resulting blood. As procedures are usually done with an endoscope any bleeding rapidly obscures any visualization of the surgical site. To surgically manipulate tissue (disintegrate, incise, elevate and dissect) and not obscure the surgical field with blood, instruments which apply various forms of energy have been developed. These energies include heat, cold (cryosurgery), radio frequency, laser light, plasma and sound. Each of these by itself has advantages and faults. In this patent we present a device that purposely combines sound energy with cold steel technique.
The earliest realization of sound's effects on solid structures dates back to the early 1900s when it was discovered that when a boat propeller was rotated at a high speed the resulting cavitation could destroy the propeller. The effect was to cause or use small vapor bubbles within a liquid. A spinning propeller or sound energy as a repetitive production of powerful positive and negative movement in a liquid stores this energy in the walls of these vapor bubbles. The life of these high energy bubbles is very short and the stored energy is released quickly as the bubble collapses. In appropriate surgical instruments the energy of the bubble collapse is dissipated in four different forms: as a concussion wave that can break down tissue, through heat that is intense for a very short time and can cause chemical reactions not otherwise possible, as micro streaming of movement on the bubble outer surface capable of cleaning a nearby surface, and as a vortex that can drill into tissue cells, known as sonoporation.
Ultrasonic devices on the market today produce enough energy to cause a controlled tissue disintegration. The ultrasound is created proximally, concentrated into a waveguide, and conducted to a distal tip where cavitation is created. As the cavitation is the only working energy in this tool, very large ultrasonic generators are needed. Usually this is done with stacks of piezoelectric ceramic discs or a magnetostrictive system. A typical piezo actuator is constructed as described by Langevin. A stack of piezo ceramic discs are squeezed tightly between a blocking mass and a condenser using a bolt. As sound energy is created it travels in both a proximal and distal direction. The blocking mass prevents the spread proximally. The energy is thus all concentrated into the condenser which narrows on its distal end. A waveguide is attached to the condenser to then carry the sonic energy to the target. As the objective is to cause resonance in the waveguide trying to condense the energy at an antinode the length of the waveguide is dependent on the frequency of the sound. To achieve high energy levels at the distal end a thick, straight and rigid waveguide is created. The material transmits sound at a relatively high speed (for example using a titanium alloy with speeds of about 6100 m/s). The goal is to achieve resonance of the waveguide and produce an antinode at the distal tip. To do this a large amount of electrical energy is required. Once the tip of the resonating waveguide is placed in contact with tissues, the sound energy enters the water based tissue and creates cavitation. The cavitation destroys or otherwise is used for surgical purposes.
The cavitation occurs as a spherical cloud around the tip of the instrument. A smaller instrument has a smaller cloud and is thus both more precise and restricted in the speed of action. Such a device is used for cataract surgery, a very precise surgery.
The CUSA (cavitron ultrasonic surgical aspirator) is used in brain surgery. A larger energy source and waveguide associated with a suction tube is used for neurosurgical removal of brain tumors. Its advantage is the destructive cavitational effect on high water content tissue like brain tumors with little effect on relatively drier tissue like normal brain tissue, collagen and blood vessel walls. The cavitation produced disintegrates the tumor and an integrated suction removes the detritus. The difference in water content results in surgical precision at lower powers.
Another surgical tool that uses ultrasound is a harmonic scalpel. A rapid longitudinal, reciprocating movement imparted into a scalpel shaped blade results in cutting of tissue. The associated heat generated causes coagulation. The cutting is very precise due to the high rate of movement and the narrow loss of cells in the kerf.
Other surgical instruments employ tissue welding and coagulation produced by sound energy reduced to heat as a waveguide transmits sonic energy to tissues. Blood vessels can be fused closed or various clips can be fused to clamp vessels.
In the early 1990s trials of the CUSA for intranasal surgery (polypectomy) were conducted. This tool was excellent at removing tissue almost bloodlessly but was exceedingly slow. Trial use of CUSA for tonsillectomy has also been published. The advantages were precise extracapsular excisions with little bleeding.
The SonoPet was introduced recently for otolaryngology work. It is also a rigid straight hollow waveguide that suctions blood and detritus. It also is marketed with a variety of rasp tips for vibratory motion and bone abrading. From a nasal surgery standpoint, it is very good for abrading through bone into the frontal sinus and between the nose and braincase, with its greatest advantage being the slow precision in dangerous areas.
A device developed in Russia and found in eastern European clinics called a Tonsillor is another high-energy ultrasonic device. It is very powerful as it too works primarily through cavitation. It is proximately bulky and has a long, relatively thick, rigid waveguide with a variety of tips. It is used near the external surface and straight into the nasal passage as it is too large for precise intranasal work deep in the nose.
Other devices have been proposed that add ultrasound to a rotating suction knife device (debrider, Hummer, and the like).